The objective of this research proposal is to gain insight into the events surrounding regression of the corpus luteum and to provide information on the endocrine and cellular events leading to this process. In particular, it is planned to test the hypothesis that regression occurs through an induced loss in luteal function as a consequence of impaired gonadotropin uptake and/or gonadotropin receptor function. In addition, the objective is to examine a possible interrelationship between estrogen and PGF2 alpha, known luteolytic agents, in regulation of gonadotropin receptor function in corpora lutea. Methods to be employed in these studies include: 1) In vivo studies on control of corpus luteum blood flow with the aid of radiolabelled microspheres; 2) In vivo studies on I125-hCG uptake by corpora lutea during development and regression; 3) Isolation and assay of luteal tissue for the gonadotropin and prostaglandin receptors; 4) Development of an immunoassay for the gonadotropin receptor; 5) Assay of cyclic AMP in isolated membrane fractions of corpora lutea; 6) Isolation and characterization of ovarian extracts for gonadotropin receptor inhibitor; 7) Development of an isolated lutea cell preparation to examine regression in vitro. With the aid of the above techniques ad methods it is suggested that the processes involved in luteolysis will be better understood and this information may lead to identification of biochemically discrete targets for examination and/or development of novel agents for fertility control.